CoSIA: Cross Species Investigation and Analysis is an R package that provides researchers with the tools to measure and visualize gene-expression metrics in order to compare across model organisms and their tissues. Specifically, CoSIA uses curated non-diseased wild-type RNA-sequencing expression data, from Bgee, to visualize a gene’s expression across tissues and model organisms. CoSIA also streamlines conversions between gene identifiers among the same species and different species.